In the foundry industry, one of the processes used for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry mix which is a mixture of sand and an organic or inorganic binder.
One of the processes used in sand casting for making molds and cores is the no-bake process. In this process, a foundry aggregate, binder, and liquid curing catalyst are mixed and compacted to produce a cured mold and/or core. In the no-bake process, it is important to formulate a foundry mix which will provide sufficient worktime to allow shaping. Worktime is the time between when mixing begins and when the mixture can no longer be effectively shaped to fill a mold or core.
A binder commonly used in the no-bake process is a polyurethane binder derived by curing a polyurethane-forming binder with a liquid tertiary amine catalyst. Such polyurethane-forming binders used in the no-bake process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 1370.degree. C. They are also useful in the casting of light-weight metals, such as aluminum, which have melting points of less than 815.degree. C. The phenolic resin component typically contains small amounts of free formaldehyde and free phenol which are undesirable. Both the phenolic resin component and the polyisocyanate components generally contain a substantial amount of organic solvent which can be obnoxious to smell and smoke during the mixing and the pouroff stages in the workplace.
U.S. Pat. No. 5,689,613 discloses polyurethane-forming foundry binders which use ester-based aromatic polyols as the polyol component of the binder. These binders are do not have any free formaldehyde or free phenol. However, they are too viscous to use without a solvent.
U.S. Pat. No. 5,688,857 discloses a polyurethane-forming cold-box binder which is solvent free and does not contain any free formaldehyde or free phenol. Although satisfactory for cold-box applications, this binder is not satisfactory for no-bake applications because early tensile strengths of cores and molds prepared with this binder were not sufficient. Consequently, there is an interest in improving the early tensile strengths for no-bake applications to allow the cores and molds to be more readily stripped from the pattern, and thus improve higher productivity.